Control-gear for hydraulic circuits



Dec. 26, 1961 A. E. R. ARNOT CONTROL-GEAR FOR HYDRAULIC CIRCUITS 4Sheets-Sheet 1 Filed June 25, 1959 Dec. 26, 1961 A. E. R. ARNOT3,914,344

CONTROL-GEAR FOR HYDRAULIC CIRCUITS Filed June 25, 1959 4 Sheets-Sheet 2.FLOLHI v WK? Dec. 26, 1961 A. E. R. ARNOT 3,014,344

CONTROL-GEAR FOR HYDRAULIC CIRCUITS Filed June 25, 1959 4 Sheets-Sheet 3W K K WW;

Dec. 26, 1961 A. E. R. ARNOT 3,014,344

CONTROL-GEAR FOR HYDRAULIC CIRCUITS Filed June 25, 1959 4 Sheets-$heet 4This invention. comprises improvements in or relating to control-gearfor hydraulic circuits.

The invention relates to hydraulic circuits of the kind in which a pumpactuates a device for utilising hydraulic fluid, in accordance with theoperation of a control-valve which can be moved to determine theutilisation. For ex.- ample' a jack may serve to utilise fluid by movinga part to and fro and the control valve may determine the direction. andvary the speed of operation of the jack.

It is an object-of this invention to provide an improved system ofcontrol for a hydraulic circuit in which less power is wasted than isusual. Usually pumps have a States Pater constant delivery and when thecontrol valve is closed to reduce the rate of utilisation, the excesspump delivery is shunted off by a relief valve. This system is verywasteful ofenergy and places unnecessary loadings on the pump, drivingmotor, and relief valve which may reduce their useful working life.

According to the present invention a system of control for an hydrauliccircuit of the kind described comprises in combination a means forcontrolling the pump to vary its rate of delivery, a control valve orvalves between the pump and the circuit in which the delivery isutilised andconnections between the control valve or valves andthe meansfor controlling. the pump, said connections being operative to vary thedelivery of: the pump according to the rate of utilisation selected bythe control valve or valves. The extent to which the delivery is variedmay be such that a small excess pressure is normally maintained andisconducted. away'by a relief. valve. In the embodiment hereinafterdescribed the means for controlling the pump to vary its rate ofdelivery operates by varying its speed. An electrical drive forthe pumpis provided and the connections between. the hydraulic con trol valve orvalves and the meansfor controlling the pump comprises switch meansoperated by the control valve or valves, andelectrical connections fromthe switch means to an. electromagnetic speed control device for thepump drive. The means for controlling pump deliver-y may howevercomprise connections-to theaccelerator of a driving engine. or the.control lever of a. variable delivery pump.

Normally, a jack piston hasv greater effective area for one directionof. movement than for the other, owing to. the piston-rod reducing theetfective area of one. face of the piston, andwill tend to move fasterin the direction for. which the area is least, as, the rate of supply isnormally constant. It is one object of the present invention toprovidemeans. to compensatefor. this tendency. The invention mayhowever. be employed, not merely for compensation, but to ensure. adesired speed. or rate ofutilisation in any device.

The following is a description by. way of example ofone arrangement. in.accordance. with the invention, as applied to an industrialreach truck.

In the accompanying. .drawings:.

FIGUREI isv arear-elevation of the truck with. certain partsbrokenaway;

FIGURE 2 is .a.plan.of.the same;

FIGURE. 3' is. an. elevation: of the hydraulic controlmechanism;

FIGURE 4 is. a-. section onthe: line 44.of- FIGURE 3;

Patented Dec. 26, 1961 FIGURE 5 is a section on the line 5-5 of FIGURE3; and

FIGURE 6 is a diagram of electrical connections.

The truck comprises a body II having forwardlyextending parallelstraddlelegs 12 close to the ground supported on front wheels 13,power-driven steerable rear wheel 14 and a pair of castoring rear wheels15, mounted on an equalising castor mounting 16.

A drivers seat 17 is set across the truck with a steering wheel 18facing the driver, which is connected to a steering linkage 19 whichgoverns the orientation of the power in the wheel 14 through alink 20.

The power-driven steering wheel 14- is operated by an electric motor inthe casing 21 below the drivers seat and the motor is controlled by anaccelerator pedal 22 which operates an electric controller in knownmanner.

Over the driver there is a guard rail 23 which is supported on tubularmetal columns 24- Which rise from the body 11.

Between the straddle-legs 12 there is a mast 25 which is supported onguides in the legsby' rollers 26 andhas also rearwardly-extendingframe-members 27 which meet one another beneath the body 11 and carryrollers to run in a central horizontal guide. The mast is moved fore andaft on the straddle-legs by a jack 28 having a jack-rod 29 which engagesa cross-member 30 behind the mast. The mast itself is tiltablerelatively to the frame-members 27 which carry the rollers 26 andtilting is effected by jack 31, one end of which is connected to thecross-member 39- attached to' the mast and the other end' of which isconnected to a leg. 31 attached to one of the members 27. The effect isthat. the mast could be tilted forwardly or rearwardly by operating thejack 31. On the mast is a rising carriage 32 which carries fork arms 33and the carriage can be elevated or lowered by jack 34 between the sidesof the mast and connected thereto by chains. Thus there are three jacksfor con-- trolling the movements of the load-carrying forks 33, namelythe jack 34 for raising and lowering it, the jack 31 for tilting themast and the jack. 28 for moving thecarriage which supports the mastforwardly or. backwardly. The three jacks are controlled by three levers35, 36, 37 in front of the operator on the line: of the steering wheel,the lever 35 which is nearest to the operator controlling the tilt-jack31, the lever 36 controlling the reach-jack 28 and the lever 37controlling; the lift-jack 34;

Power for the jacks which are controlled by these levers is supplied bya pump 38 driven by an electric motor 39 below the footrpl'at'e 4-0 infront: of the driver. It is the pump: 38 which is controlled accordingto the present invention so as to vary the rate: of delivery andthemeans of control are shown in FIGURES 3, 4 and 5, taken in conjunction:with the electrical circuit of FIG- URE 6.

It will be appreciated that the jack-cylinder 28 and piston rod 29 whichprojects forwardly from the cylinder into engagement with the travellingmounting of the mast,- constitute a construction in which. the front.end of the jack cylinder is of smaller capacity than the rear. end andif. operated by a motor-driven pump such as 38' through a normal controlvalve, the movement. of' retraction will be faster than the-movementofadvance; but this is undesirable as, if goods are deposited on. the forkarms 33 of the carriage 28 and the retractionmovement is started toofast, the goods may slip off the fork arms" or: tip over;

The reachvalve plunger 136 is of normal: type and is operated by thecontrol lever. 36 which is pivoted on a. cross bar 40- and can bemovedtowards the front of the truck foradvancing the mast 2'5 and towards therear for retracting it. The lever- 36 has a horizontalarm: 41 which:operatesa connecting; rod 42 pivoted to the plunger 136 at 43. Theplunger 136 serves to operate lift valvcstirr.

the interior of the valve casing 44 which valves direct the output ofthe pump 38 in the first case to the rear end of the jack 28 and in thesecond case to the front end.

According to the present invention, the motor 39 provided for drivingthe pump 38, is capable of running at two different speeds proportionedrespectively to the output required for the forward movement and thelower output required for the retraction.

Adjacent to the operating lever 36 are two microswitches 45, 46, thelatter closed when the lever is moved to the forward position and theformer closed when it is moved to the retraction position. Theconnections are shown in FIGURE 6. In FIGURE 6 the battery 50 whichoperates the truck (and which is located in 2 L- shaped battery cases51, 52, seen in FIGURE 2) is connected each to one terminal by a line 53to one terminal of the motor 39 which has a series field winding 54. Theother terminal of the motor is connected by a line 55 to the contacts56, 57 and a solenoid switch 58 and then through a fuse 59 and line 60to the other terminal of the battery. The motor has also a shunt fieldwinding 61 connected to the contacts 62, 63 of a second solenoid switch64 and the contacts of the solenoid switch are connected by a line 65 tothe other terminal of the battery. Thus the solenoid switch 58 canswitch the motor on to run as a series motor and the solenoid switch 64can bring into circuit the additional shunt winding 61 to reduce themotor speed. The solenoid windings of the switches 58-and 64 areconnected on the one hand by a line 66 to the line '60 and one side ofthe battery and on the other hand by lines 67, 68 to the micro-switches46, 45, respectively.

Connected to the same terminal of the battery as the line '53 there is aline 69 which extends through a fuse 47 and main switch 48 to a line 70running to the circuit of the traction motor of the truck. There is alsoa line 71 to the other terminal of the traction motor which extends fromthe line 60 before-mentioned. The circuit of the traction motor does nothere concern us but there is a branch 72 from the line 69 through aswitch 73 to one terminal of the micro-switch 46. Similarly, there is abranch 74 from the line 67 to a terminal of the microswitch 45. Inoperation, the micro-switch 45 is normally closed and the micro-switch46 is normally open. The mechanical connections between themicro-switches and the levers will now be described, taking first theconnections from the lever 36 so that the operation of thereach-mechanism can be followed out completely. Each of the levers 35,36, 37 has a hub made of a rectangular piece of metal and the hubs arenumbered in FIGURE 3, 75, 76, 77. Each of the levers proper is welded toits hub as can be seen in FIGURE 5, where the connection of the lever 35to its hub 75 appears. The hub has an antifriction bush 78 and rocks onthe cross-bar 40 which extends beween a fixed frame member 79 at oneside of the apparatus and another frame-member (not shown) at the otherside of the apparatus. Above the cross-bar 40 there is a cross-bar 80and below it there is another crossbar 81. The cross-bar 80 is securedin the frame-member 79 by a set-screw 82 and extends right across theapparatus to the second frame-member to which the bar 40 is attached atits right-hand end, as viewed in FIGURE 3. The cross-bar 81 is similarlysecured by a set-screw 83 but does not extend right across theapparatus. On the contrary it is overhung and stops just short of thevalveoperating member 42. On the cross-bars 80, 81 there are mountedrocking sleeves 84, 85 respectively. Immediately below the micro-switch46 the sleeve 84 carries a depending plate 86 which has a lateral shelf87 (best seen in FIGURE 4). The shelf 87 carries an adjustable tapet 88which operates a sliding head 89 on the microswitch 46. The head 89 ismounted on a cam-rod 90 which is urged downwardly by a spring 91 andwhich has a sloping cam face to engage the operating lever 92 of themicro-switch 46. Thus, if the sleeve 84 is rocked clockwise, as viewedin FIGURE 4, it will operate the microswitch. In a similar way thesleeve 85, which is below the crossbar 40, carries an upwardly extendingplate 93 having a shelf 94 in which is a tappet 95 for operating themicro-switch 45. The plate 93 extends along the whole length of therocking sleeve 85 and one corner of it is in front of a screwed stop 96carried on the hub 76 below the bar 40. The stop 96 is seen in dottedlines in FIGURE 3 of the drawing and a similar stop 97 on the hub 75appears in FIGURE 5 of the drawing. The effect of the screwed stop 96is, if the lever 36 is rocked toward the front of the truck, to engageand tilt over the plate 93 on the rocking sleeve 85 and to operate theswitch 45. On the rocking sleeve 84- there is a downwardly dependingplate 98 which lies in front of the screwed stop 99 on the upper part ofthe hub 76 of the lever 36 and, if the lever is rocked towards the rearof the truck, the effect is to tilt the plate 98 and rock the sleeve 84so that it operates the micro-switch 46 to close it. There is a furtherdownwardly depending plate 100 on the rocking sleeve 84 which dependsfrom it further than the plate 98 and can be engaged by a screwed stop101 on the lower part of the hub 76 of the lever 36. The effect of thescrewed stop 101 is to engage the plate 100 and rock the sleeve 84 whenthe lever 36 is moved toward the front of the truck for advancing thereach-jack 28 and thereby to close the micro-switch 46 at the same timethat the valve plunger 136 is operated to move the reach jack in thedirection to advance the mast to the front end of the truck. Thus,whether the lever 36 is moved forwardly or rearwardly, the micro-switch46 is closed either by the stop 101, acting on the plate 100, or by thestop 99, acting on the plate 98, but in the event of the lever beingmoved further forward, the stop 96 also rocks the plate 93 and therocking sleeve 85 and operates the micro-switch 45.

We are now in a position to consider the operation of the connections,which are shown in FIGURE 6. If the lever 36 is rocked forwardly, themicro-switch 46 will first be closed and on further movement the switch45 will be opened. Consequently, current will follow through the line69, fuse 47, switch 48, switch 73 and line 72 to the micro-switch 46,which, being closed, will energise the line 67 and the solenoid windingof the electro-magnetic switch 58 thereby closing the contacts 56, 57and starting up the motor 39. If the micro-switch 45 is opened, thecontacts 62, 63 will not be closed and the pump will run to a higherspeed to advance the jack 28 at its full rate. If, on the other hand,the lever 36 is moved rearwardly to retract the jack 28 the stop 99 willact on the plate 98 to rock the sleeve 84 and close the micro-switch 46.At the same time the stop 96 on the hub 76 of the lever 36 will moveaway from the plate 93 and the microswitch 45 will not be operated, butwill remain closed and will energise the solenoid switch 64 and closethe circuit of the shunt Winding 61, thus ensuring that the motor runsat the lower speed, which is necessary on account of the smaller area ofthe piston of jack 28 on its retraction stroke. The shunt winding 61 iscalculated to give the appropriate speed.

The lever 37 which operates the lift-jack 34 has on its hub two screwedstops 102, 103. The stop 102 rocks the plate 98 and operates themicro-switch 46 and the stop 103 rocks an upward extension 104 of theplate 93 and operates the micro-switch 45. If the lever 37 is movedrearwardly it will therefore operate both the micro-switch 45, 46 andthe pump motor 39 can run at its highest speed for raising the ram ofthe jack 34 and lifting the forks 33. This is necessary on account ofthe higher capacity of this jack. On the other hand, if the lever 37 ismoved towards the forward part of the truck, it will not operate eitherof the micro-switches, the pump will not work and the mast with its forkwill be allowed to descend by gravity. As will be obvious, the lever 375 operates a connecting rod 18:5 which operates a valve member 106.

The lever 35 has on its hub two stops, one of which 97 has already beenreferred to and the other of which is numbered 107. These appear inFIGURE 5- of the drawing and they both operate on the plate 1% which haspreviously been described. Therefore, they both serve to close themicro-switch 46, leave the micro-switch 45 untouched, and in whicheverdirection the lever 35 is moved, the motor will be operated at a slowerspeed. This lever is for operating the tilt-jack 31 by a connecting rod168 and valve-mernber 199 and the tilting of the mast is thereforeeffected by a slow movement; this is desirable in either direction.

It will be apparent from the above that the mechanism shown enables anylever so to be interlocked with the micro-switches that the movementefiected by its valve in either direction is a preferred rate. Thus themotor 39 is run automatically at the appropriate speed to pro duce apump output which will cause the desired movements to be as required ineither direction.

If it were desirable to retract more slowly than to advance, the motorspeed control would be adjusted accordingly.

I claim:

1. A hydraulic system comprising a hydraulic pump, a plurality ofdevices connected in parallel to the pump for utilizing the pump output,a separate hydraulic control-valve in series with each device, leversfor operating each control-valve, an electric motor for driving thepump, a motor-starting micro-switch and a motor-regulating micro-switchconnected to the electric motor for starting the motor and forregulating the speed of the motor, two rock-shafts adapted to actuatethe two microswitches respectively, plates rigidly secured to therockshafts and tappets mounted on the control-valve levers to engage theplates so that the micro-switches are actuated by movement of thecontrol-valve levers.

2. A hydraulic system as claimed in claim 1 wherein the control-valvelevers are pivoted about an axis and wherein tappets are mounted on thelevers above and below the axis so that the micro-switches are actuatedby pivotal movement of the levers about the axis in both directions.

' 3. A hydraulic system comprising a hydraulic pump, a device forutilizing the pump output, a hydraulic control valve connected in seriesbetween'the pump and said device, control-valve operating means, anelectric motor for driving the pump, said motor having a field-modifyingwinding, an electro-magnetically actuated switch for bringing saidfield-modifying winding into operation, motor-starting switch-meansactuated by said controlvalve operating means and motor-regulatingswitch means also actuated by said control-valve operating means forcontrolling said electro-magnetically actuated switch to modify themotor speed.

References Cited in the file of this patent UNITED STATES PATENTS1,885,077 Cannon Oct. 25, 1932 1,928,915 Stout Oct. 3, 1933 2,135,157West Nov. 1, 1938 2,316,926 Willett Apr. 20', 1943 2,330,739 Piron Sept.28, 1943 2,374,909 Williams May 1, 1945 2,425,391 Parsons Aug. 12, 19472,609,665 Rappl Sept. 9, 1952

